The following abbreviations which may be found in the specification and/or the drawing figures are defined as follows:
3GPP Third Generation Partnership Project
CIO Cell Individual Offset
CPICH common pilot channel
CSG closed subscriber group
DCH dedicated channel
DL downlink
E-DCH enhanced uplink dedicated channel
E-UTRAN Evolved Universal Terrestrial Radio Access Network
HetNet heterogeneous network
HPN high power node
HS-DPCCH high speed dedicated physical control channel
HS-DSCH high speed downlink shared channel
HSDPA high speed downlink packet access
HSPA High Speed Packet Access
IE information element
ISCP interference on signal code power
LPN low power node
LTE Long Term Evolution
MR multiflow
RAT radio access technology
RSCP received signal code power
SHO soft handover
UL uplink
UMTS Universal Mobile Telecommunications System
UTRAN UMTS Terrestrial Radio Access Network
Continuing expansion of mobile and other wireless communications is rendering the available radio spectrum more crowded and this trend is expected to increase in the near term as greater volumes of data are wirelessly exchanged. One recent approach to increase the ability of network operators to handle this increased traffic is to deploy so-called heterogeneous networks (or “HetNets”). In a heterogeneous network, there is at least one conventional cell, commonly termed macro cells or the like, and one or more smaller cells, sometimes termed micro, pico or femto or local cells or the like, which are (fully or partially) within the coverage area of the macro cell(s) and which operate with various levels of coordination with the macro cell(s). The smaller cell or cells can be used for example to extend the coverage area of the macro cell(s), either to extend range or to fill holes in coverage provided by the macro cell(s), and to improve capacity.
In a heterogeneous network or HetNet, a macro cell network node (which may for example be a base station of the macro cell) typically transmits with a much higher power than the network node(s) of the smaller cell(s), and so the macro cell coverage area is much larger than that of the smaller cell(s). Some HetNet deployments have the macro cell(s) and the smaller cell(s) on different frequency bands, such as a primary versus a secondary component carrier, whereas others have the one or more smaller cells operating on the same frequency band as the macro cell. The latter deployment where the frequency band is shared is sometimes referred to as a “co-channel HetNet” or similar.
In the Third Generation Partnership Project (3GPP) document R1-110687 entitled “Interference Issues in Heterogeneous Networks for HSPA” by Qualcomm Inc. (3GPP TSG WG1 Meeting #64; Taipei, Taiwan; 21-25 Feb. 2011), there is a discussion of some of the issues concerning co-channel HetNets. HSPA in the title refers to the High Speed Packet Access radio access technology which is a 3G enhancement, but the issues identified there are in general applicable to other radio access technologies, such as for example the Long Term Evolution (LTE) of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) technology. Introduction of the low power node(s) of the small cell(s) to the macro cell brings challenges in terms of reliability of the uplink (UL) control channel as well as interference management between the low power node(s) of the small cell(s) and the high power node or nodes of the macro cell. More specifically, an UL imbalance caused by the transmit power difference between the small and macro cell is discussed, which can cause unreliable UL control channel decoding in the serving cell when the serving cell is the macro cell (the control channel specifically being the high speed dedicated physical control channel (HS-DPCCH) in this document R1-110687); there can be excessive UL interference from the macro cell to the low power small cell; and there can be excessive UL interference in the other direction from the small cell to the macro cell.
More generally, there may be an uplink (UL) and/or a downlink (DL) imbalance in a HetNet arising from the transmit power difference between the low power network nodes of the small cell(s) and the high power network node(s) of the macro cell, which can give rise to various problems.